1. Field of the Invention
The present invention relates to a solid-state image sensing device and an image sensing system and, more particularly, to a solid-state image sensing device which can capture a moving image and a still image and an image sensing system having the same.
2. Description of the Related Art
A digital camera using a solid-state image sensing device which can capture both a still image and a moving image has become popular nowadays. To meet a demand for still image capturing with high image quality/high resolution, information on pixels in a number larger than that of pixels read out in moving image capturing is necessary. Although moving image capturing requires pixels fewer than those in still image capturing, a specific number of frames (e.g., 30 frames per second according to the NTSC standard) need to be recorded in one second. For this purpose, moving image capturing generally consumes a relatively large power. To cope with this, there is a method of reducing the power consumption by thinning upon reading out pixels from a solid-state image sensing device or dropping the readout clock rate in the moving image capturing mode (Japanese Patent Laid-Open No. 2004-158958).
However, the number of pixels to be read out is specified by the readout standard in moving image readout (moving image capturing), so the thinning ratio cannot deviate from the readout standard. If the clock rate is dropped in moving image readout, it is necessary to provide an oscillator for generating a still image readout clock and an oscillator for generating a moving image readout clock. It is also necessary to provide a complicated circuit to prevent any trouble upon frequency switching.